1. Field of the Invention
The invention is based on a method for electrostatically charging up solid or liquid particles suspended in a gas stream.
2. Discussion of Background
In electrostatic dust filters, the nature and manner of the electrical charging plays an important role. Inter alia, they are determining factors for the dimensioning and mode of operation of the filters. If dust is to be charged up electrically this is done, as a rule, by passing a corona discharge through it. The maximum achievable charge is then proportional to the applied field strength, and the rate of charging up is proportional to the ion density. As a rule a high charge is desired, and there must therefore be a high field strength.
However, this has consequences in two respects:
(a) The ion density falls since the drift velocity increases with the field strength. This results in a longer charging time (larger equipment, poorer ion utilization factor since the probability of collision with the particles decreases, from which an energy loss accures). PA1 (b) The charged particles are subject to a deflection force proportional to the field which attracts the particles to the wall and results in their deposition.
Arrangements have already been proposed in which the gas stream loaded with particles is first passed through a device with corona discharge and then between two parallel plates to which an electrical alternating field is applied. In this process the intention is to achieve an agglomeration as a result of particles of different size and velocity striking each other. The frequencies of the alternating field in this case are substantially below 1 kHz (cf. Kobashi and Masaaki, "Particle agglomeration induced by alternating electric fields", Degree date 1979, University microfilms international, 300 N. Zeeb Road, Ann Arbor, Mi 48106.
These violent methods and devices do not achieve the object in an optimum manner. The expenditure is considerable in terms of volume and costs. There is therefore a need to simplify and to refine the existing methods.